This relates generally to connectors and more particularly to fiber optic connectors and methods for joining together two optical fibers.
Data transmission over optical fibers offers many significant advantages compared with metallic conductors, including: long distance transmission without the need for repeaters, immunity from electromagnetic interference, cross-talk and ground lop, high bandwidth capabilities, small size and weight, high degree of intercept security and dielectric isolation, and long term cost reduction. These desirable features of optical fibers have strongly stimulated efforts both in fiber optics and in supporting technologies such as fiber optic coupling.
Connectors for joining together optical fibers are critical to systems which transmit data over optical fibers. If such connectors are not efficient, fiber optic data transmission would be a less feasible alternative to transmission over metallic conductors. Inefficient connectors can make it necessary to manufacture unbroken cables miles in length or to detect and actively reamplify the transmitted signal at every break in the optical fiber. Repeaters are devices which provide such detection and reamplification. However, they are expensive active components which decrease the reliability of the system and add to the energy consumption of the system. Thus, efficient passive connectors which are also cost effective are an economic necessity.
Practically all devices which employ optical fibers can benefit from improved cost effective connectors. For example, the connectors which form part of a star-coupler typically contribute from about one-third to one-half of the entire cost of the star-coupler. Thus, a decrease in the cost of such connectors can provide a significant decrease in the cost of a star-coupler employing a number of such connectors.
Difficulty has been encountered in providing proper alignment between the two optical fibers joined by a connector. Such alignment is critical in an axial direction (end separation) as well as in a radial direction (lateral offset). Improper alignment in either of these directions produces significant losses.
Further difficulty has been encountered in the assembly and connection of optical connectors. Known connectors which connect single optical fibers are typically provided with a sleeve which is insertable into the connector. It is within this sleeve that the two fibers actually interface with each other. However, these sleeves are quite small and are prone to loss. To further complicate matters, these sleeves have very thin walls. Thus a connector may be used without the sleeve unbeknownst to a user and yet transmit some amount of light. This results in poorly operating or inoperative devices. In fact, devices incorporating such connectors have been returned to manufacturers as defective when in actuality, the consumer has assembled the connector without the sleeve.
Additionally, these sleeves are generally constructed from stainless steel and the bore through the sleeve is often displaced from the true center of the sleeve. This is due largely to the "walking" of a drill bit away from the desired location of the bore as the drilling process is initiated. Proper alignment is practically impossible without the sleeve. Furthermore, the bore through these sleeves is generally tapered. The actual length of the portion of the bore which has a diameter equal to the diameter of the fiber element is significantly less than the length of the alignment sleeve, perhaps only one-fifth of such length. This reduces the effective length of the sleeve which maintains the fiber in a desired concentric position, thus contributing to inaccurate alignment of the fibers. Furthermore, optical fibers are often attached to connectors by crimping a metallic sleeve of the connector around the optical fiber, however, this can damage the optical fiber.
Furthermore, known connectors are unnecessarily complex, thus also contributing to the difficulty of properly assembling the connector and connecting it to a mating connector, as well as adding to the cost of the connector.
Another disadvantage of known connectors is their lack of adjustability. Although maximum light transfer and low loss are generally desirable, it is advantageous at times that the connector be adjusted to increase loss and reduce light transfer. For example, light input to a star-coupler is often output non-uniformly to the N optical fibers of the coupler due to the structure of the mixing element employed in the coupler as well as nonuniformity among the optical fibers. In such circumstances it is desirable to adjust the light loss in each fiber so that light levels are approximately uniform in each fiber.